Boolossus

Boolossus is a humongous Boo, and the boss of Pumpkin Boneyard's tower and castle. He is fought in a dark hallway, and will continuously advance towards the players. Mario, Luigi, and the Toads must throw Glow Blocks at it to force it back. The end of the hall contains a button that, when pressed, will turn the lights on and defeat Boolossus.